Direct Photon Production from Positive and Negative Pions and Protons at 200 GeV/c (NA3 Collaboration)

Abstract

Direct photon production has been studied by the NA3 Collaboration at the CERN SPS using negative and positive beams at 200 GeV/c incident on an isoscalar Carbon target. The experiment, completed in 1985, published the first fixed target measurements of the asymmetry of prompt photon production by negative and positive pions. The experiment was sensitive to photons with 2.5 ≤ PT ≤ 6.0 GeV/c and C.M. rapidity — 0.4 ≤ Y★ ≤ 1.2.

NA3 final results on: a) direct photon production by π ± and protons b) charge asymmetry measurement on direct photon production from π − and π + c) direct photon pair production by π ± and protons d) π° production measurements by π ±, K + and protons are recalled, commented on and compared to data recently published by other fixed target experiments.

For a detailed discussion on this subject, see the review of ref. [1].Google Scholar

12.

Four small beam chambers used in conjunction with a beam dipole measured the beam momentum with a precision AP/P = 0.8%. The momentum after the radiator was moreGoogle Scholar

precisely measured by the NA3 S.C. dipole. A set of three movable dipoles placed in front of the spectrometer allowed the vertical deflection of electrons so leaving “isolated” the radiated photon. For more details see also the Thesis of ref. [8].Google Scholar

13.

In reality a small (10%) correction to the pair energy measured by the spectrometer is given by the pair bremsstrahlung in the converter itself. The energy of bremsstrahlung photons is measured in the calorimeter.Google Scholar

14.

The physics results of the WA70 Collaboration used for the comparison are from:Google Scholar